Heat the oil in a large,pot over medium low. Add the onions and saute for at least 10 minutes, stirring them around frequently. When the onions soften, add the herbs and paprika and saute for another 5 minutes, stirring all the while.
Add the garlic and stir. Add the carrots and celery and cook for another 5-10 minutes, until all vegetables are soft.
Now add the tomatoes and stir to coat vegetables. Cook the tomatoes for 5 minutes. Add drained lentils and stir to coat in the vegetables, oil and tomatoes.
Add the stock, give the whole mix a good stir and bring to a boil. Once boiling, return pot to a simmer, cover with a heavy lid and allow to cook for 30 minutes or until the lentils are soft. Season to your liking.